Hydraulic (e.g., hydratable) cementitious compositions, such as mortar (cement, small particulate, e.g., sand, and water), or concrete (cement, small particulate, large particulate, e.g., gravel, and water), are used extensively in forming, either alone as a concrete formation or in combination with other elements as a mortar and brick formation) architectural structural formations. These compositions have certain properties that substantially affect their durability, including shrinkage that occurs during drying and curing of the cement composition.
Conventional hydraulic cement compositions display a decrease in volume with setting and drying of the cast composition Although the magnitude of the volume decrease is normally small, it is of extreme importance. This shrinkage results in cracks and other defects that decrease the service life and durability of the resultant structure. The cracks provide a path for air to penetrate into the structure, promoting carbonation of the cement and corrosion of the metal reinforcing bars contained therein. Further, the cracks provide a means for water to seep into and through the structure. Such water entry further deteriorates the structure through freeze-thaw cycling pressures exerted on the cement structure over its life. It is highly desired to provide cements and cementitious mixtures that exhibit high strength and are not subject to deterioration effects due to shrinkage.
With respect to overcoming the drying shrinkage of cement compositions (such as concrete mixtures), the literature teaches that various oxyalkylene adducts are suitable for this purpose. For example, U.S. Pat. No. 3,663,251 teaches a shrinkage reducing additives of the general formula RO(AO)nH, in which R may be a C1-C7 alkyl or C5-C6 cycloalkyl radical, A may be a C2-C3 alkylene radical, and n is 1-10. Other references concerning shrinkage reducing additives are identified in U.S. Pat. No. 5,603,760, which is incorporated herein by reference.
The present inventors have discovered surprisingly that oxyalkylene compounds which provide shrinkage inhibition in cements and concretes have a tendency to generate dust particles on the surface of the resultant cement or concrete structure. This can create an undesired problem, for example, in applications such as self-leveling concrete or foundations, against which or upon which coatings or adhesives are applied to attach tiles, wood flooring, carpeting, or other surface treatments. The problem is caused by the dust which tends to defeat the ability of the coating or adhesive to attach to the resultant structure. Accordingly, the present invention provides a novel admixture, method, and cementitious composition wherein the formation of surface dust is prevented or minimized.